Adult aging represents a balance of decline and compensation. This grant investigates the interacting effects of adult aging, age-related declines in hearing acuity, and engagement of the neural networks that underlie the ability to comprehend spoken sentences. Good progress has been made in understanding this balance at the behavioral level, but far less is known about the underlying neural substrates that carry these effects. In this grant we address the neural basis for aural sentence comprehension and how this is affected by perceptual effort due to reduced hearing acuity, and central cognitive loads such as those imposed by syntactic complexity, speech rate, working memory demands, and the semantic and syntactic ambiguities that occur in everyday discourse. We are guided by a novel model of sentence processing that implicates several dissociable neural substrates that become engaged depending on the cognitive and perceptual demands of the materials being processed. Our subjects will be healthy young and older adults with good hearing acuity and with mild-to-moderate hearing loss. We test our neurocognitive model using novel imaging methods that combine fMRI BOLD activation studies with structural imaging of gray matter thickness and white matter projections that integrate cortical areas. We hypothesize that this model of selective working memory and decision-making during sentence processing partially breaks down during aging because of limited white matter projections between brain regions, and cortical thinning in dorsolateral prefrontal cortex. We also assess potential compensatory mechanisms. Aim 1 examines effects of syntactic complexity and speech rate, Aim 2 specifically manipulates working memory load within sentences, and Aim 3 investigates decision-making needed to resolve lexical and syntactic ambiguities encountered during sentence processing. The proposed studies will close a critical gap in our knowledge of the interacting effects of cognitive aging and age-related hearing loss on everyday speech comprehension in older adults. This work may also serve as a framework for early detection of pathological change as it affects language comprehension in the aging brain.) )